//
// Created by wze-zero on 2024/9/11 011.
//
#include <iostream>

using namespace std;

int main() {
    int num, sum = 0;
    cin >> num;
    for (int i = 1; i < num + 1; ++i) {
        i % 2 == 0 ? sum -= i : sum += i;
    }
    cout << sum << endl;
    return 0;
}